It is customary in the mining industry to agglomerate or pelletize finely ground mineral ore concentrate so as to facilitate the handling and shipping of the ore. Similarly, in the benefication of iron ore for use as feed to an iron making process, unit operations such as crushing, concentration, separation and agglomeration or pelletization are employed. The agglomeration of concentrated ore may include the production of ore pellets, sinter, nodules and briquettes. The agglomerated or pelletized ore for iron making must provide acceptable gas permeability (gas-solid contact) in a blast furnace. Sintering and pelletization are the most widely used forms of ore agglomeration in the iron making industry.
In the process of agglomeration or pelletization, grinding and screening is followed by the production of ore balls using equipment such as a balling drum or a disc pelletizer. Ore balls formed in the balling drum or disc pelletizer must be stable, that is resistant to attrition in the subsequent handling processes. Filler and/or binding agents are often added to the feed to aid balling and hold the mineral ore concentrate together as pellets until after firing. Typical additives include fillers such as lime, burnt lime, bentonite clay, olivire or water soluble polymers. In addition to such binding aids, adjustment of the moisture content of the ore concentrate also takes place typically by adding moisture via water sprays.
After balling operations, the pellets are formed, but they are still wet. These pellets are commonly known as "green pellets". The green pellets are transported to a kiln and indurated by heating in stages to an end temperature of approximately 2800.degree. F. After heating, the fired pellets are extremely hard and resist cracking upon being dropped and resist crushing when compressed.
The permeability of the treated pellets is important. Thermal shock resistance is a factor which is related to the permeability of the treated pellets. Increases in permeability increased the thermal shock resistance by improving the pellets ability to resist internal pressures created by the sudden evaporation of water when the pellet is heated. If the pellets are not sufficiently permeable, the pellets have an increased tendency to shatter upon rapid heating. This causes a concurrent increase in the amount of fines or coarse particles in the agglomerated ore. In addition, the indurated mineral ore must exhibit sufficient gas permeability to provide the required gas-solid contact in an iron making blast furnace.
The addition of materials to an ore concentrate prior to agglomeration is known. Moisture in the form of water sprays is often added to ore concentrate to facilitate agglomeration. Binding agents such as bentonite, burnt lime as well as organic binders such as poly(acrylamide), polymethylacrylamide, carboxymethylcellulose, hydroxyethylcellulose, carboxyhydroxyethylcellulose, poly(ethylene oxide), guar gum and others may be added to ore concentrate. In some operations, organic binders are favored over bentonite because the organic binders do not increase the silica content of the pellets. Organic binders will burn out during pellet firing operations and cause an increase in the porosity of the pellets.
U.S. Pat. No. 3,893,847, Derrick, discloses a binder and method for agglomerating mineral ore concentrate. The binder used is a high molecular weight, substantially straight chain water soluble polymer. The polymer is used in an aqueous solution. The polymers disclosed as useful in Derrick include copolymers of acrylamide as well as other polymers. The polymers of Derrick are employed in an aqueous solution.
U.S. Pat. No. 4,802,914 to Rosen et al., discloses a process of agglomerating a mineral ore concentrate in which a water soluble, high molecular weight polymer binder is employed. The polymer is applied as a water-in-oil emulsion, or a dispersion of fine polymer particles in oil or as a dry powder. The disclosed polymers include water soluble homopolymers, copolymers, terpolymers, and tetrapolymers. Suitable polymers include synthetic vinyl polymers and other polymers as distinquished from derivatives of natural cellulosic products.